1. Field of the Invention
This invention relates to a method and apparatus for connecting the ends of a pair of oval duct sections and more particularly to a duct joint frame assembly for connecting the ends of oval ducts that includes a plurality of frame sections with connecting end portions and connector pieces connecting the frame sections to provide a gap therebetween.
2. Description of the Prior Art
It is well known to connect the ends of adjacent rectangular heating and air-conditioning ducts by a joint assembly secured to the ends of the adjacent duct members.
U.S. Pat. No. 3,415,543 discloses a hollow coupling frame for connecting a pair of rectangular duct sections. The frame includes a pair of reversely folded legs on one side thereof which define oppositely disposed channels for receipt of the sections to be joined. The legs end in angularly related laterally disposed locking lips, which extend back toward the legs to engage and lock the sections within the channels.
U.S. Pat. No. 3,630,549 discloses a duct joint connector for rectangular ducts which includes a rectangular inner frame positioned between adjacent rectangular ducts so that the duct ends abut the frame. The rectangular ducts are secured to the frame by means of external cleats. The corners of the rectangular frame are enclosed by end caps, and mastic may be pumped into the frame to seal air gaps between the ducts and the frame.
U.S. Pat. No. 4,046,409 discloses an arrangement for joining rectangular ventilation ducts. A first and second member are connected with a first duct end and a second duct end, respectively. The second member is provided with an upright stiffening leg and a horizontal leg terminated by a hook-shaped member, which can be snapped over a raised edge of the first member. The first member comprises a horizontal lip which is received by the second member.
U.S. Pat. No. 4,410,206 discloses a flange connection for rectangular air-conditioning ducts. The flange connection includes eight pieces of open-sided box girder, four of which are slipped onto and fixed to each of two rectangular ducts to form frames thereon. The two frames are then bolted together. Angle pieces are inserted into the frames at the corners and bolted to the frames to produce the desired sealing force between the frames.
U.S. Pat. No. 4,508,376 discloses a flange type duct joint assembly that includes a pair of frame members secured to the ends of adjacent rectangular ducts. The frame members have flange portions secured to each other by angular corner pieces having rearwardly curved or displaced flange portions operable to facilitate an air-tight seal between the ends of the duct sections and the frame members.
U.S. Pat. No. 4,509,778 discloses a duct joint assembly for sealingly connecting the ends of a pair of rectangular sheet metal duct sections that include clamps for both connecting adjacent corner pieces which are part of the joint assembly and exerting sealing forces upon the corner pieces.
Assemblies for use in connecting the ends of rectangular ducts are also disclosed in the U.S. Pat. Nos. 4,542,923 and 4,558,892. The duct assemblies disclosed in these patents each include a plurality of individual frame members secured to the ends of adjacent rectangular ducts. Angular corner pieces are inserted into the ends of adjacent frame members, and the adjacent frame members on opposing duct ends are secured together by means of a clamp.
U.S. Pat. No. 4,566,724 discloses a duct joint frame for connecting rectangular duct sections that includes a plurality of flange members positioned oppositely of one another on the ends of the pair of generally rectangular ducts. Each flange member includes a stop arranged to engage a plurality of protuberances on the inner surface of the duct adjacent the duct end portion to prevent retraction of the duct end portion from the flange member. Angular corner pieces extend into the ends of the flange members to connect adjacent flange members and form a frame around the respective duct end portions.
Assemblies for connecting the ends of rectangular duct sections are also disclosed in West German Patent Nos. 2,434,160 and 2,758,295. The assemblies disclosed in these patents each include a plurality of frame members which are slipped onto the ends of the opposing duct sections, and corner pieces which are inserted into the adjacent frame members on each duct. The corner pieces are bolted together to connect the adjacent duct sections.
Although the above listed patents each disclose an apparatus for connecting generally rectangular duct sections, it is also known to provide an apparatus for connecting the ends of generally circular duct sections.
U.S. Pat. No. 3,512,805 discloses a flexible strip for connecting the ends of generally circular ducts. The flexible strip includes a pair of longitudinal grooves adapted to receive the ends of the circular ducts therein. Protuberances on the outside surfaces of the circular ducts engage the longitudinal grooves to prevent retraction of the circular ducts from the strip after assembly.
U.S. Pat. No. 3,791,681 discloses a device for establishing a sealing connection between the ends of tubular members. The ends of the tubular members are bent outwardly, and a sealing member is positioned between the outwardly bent ends of the adjacent tubular members. A connecting strip having a substantially U-shaped cross section is forced over the outwardly bent ends of the tubular members to clamp the tubular member ends against the sealing member.
U.S. Pat. No. 4,418,948 discloses an elastic coupling for joining two pipes or tubes carrying a pressurized fluid. The coupling includes a plurality of elastic ring segments each having an annular cross section and a clamping collar. The pipes or tubes to be connected each include an outwardly extending rim or flange around the circumference of the edge of the pipe. The pipe flanges are arranged to receive the elastic ring segments. After the elastic ring segments are placed in surrounding relationship with the pipe flanges, the clamping collar is clamped down into contact with the ring segments causing the cross section of the ring segments to contract. As the ring segments contract, the pipe flanges are moved toward one another to compress a seal disposed intermediate the two flanges.
U.S. Pat. No. 4,516,797 discloses a flanged ring for connecting sheet metal tube sections. Each flanged ring includes a securing flange which protrudes radially outwardly from the tube section, an arm projecting from the inner end of the securing flange and a ring land bent obliquely outward from the arm toward the securing flange. The outer diameter of the ring land is selected such that when it is driven into the end of the tube, it is prestressed and thus produces a joint between the flanged ring and the tube. To connect a pair of sheet metal tube sections, a pair of flanged rings are secured to the ends of adjacent circular ducts, and the securing flanges of the adjacent flanged rings are fixed firmly to one another by means of a screw connection, clamp or the like. A German publication identified as "Metu System 61" illustrates a flanged ring for connecting the ends of circular metal ducts and is similar to the disclosure of U.S. Pat. No. 4,516,797. There is also a Canadian publication by Titan Steel Corporation which illustrates a similar product.
An oval duct is formed from a circular duct having either a spiral seam or a longitudinal seam that is grooved or welded. The circular duct is formed in sections of a preselected length. To form an oval duct from a circular duct, illustrated in FIG. 1, a pair of elongating dies are positioned in the circular duct. The dies have an arcuate configuration which has a semi-circular dimension that determines both the height and the width of the oval duct. In fabrication, the semi-circular dies of a preselected size are moved away from each other, as illustrated in FIG. 2, to form the oval duct with the preselected transverse dimension including the height and width and the preselected arcuate end portions. It will be appreciated that the transverse dimensions of each of the oval duct sections will vary within limits due to the manner in which the circular spiral or longitudinal seam ducts are formed and the manner in which the circular ducts are deformed to form the oval ducts.
As illustrated in FIG. 3, sections of the oval duct have been connected in the past by means of an oval coupling positioned within the end portions of the oval duct sections. It is also known to provide a deep drawn beveled portion on the oval coupling to serve as a reinforcing means for the ends of the ducts and the coupling. The oval coupling may be formed from a single strip of metal with the three edges welded to each other or from a plurality of sections each having their adjacent edges welded to each other to form a unitary coupling having preselected dimensions.
It is also known to connect oval duct sections by means of oval L-shaped flanged members secured to the ends of the oval ducts and the flange members connected to each other by a plurality of bolts extending through apertures in the upstanding legs of the oval flange connectors as illustrated in FIGS. 4 and 5.
FIG. 6 illustrates another known coupling member for oval duct sections wherein the edges of the oval ducts are flanged outwardly and L-shaped flanged members are slidingly fitted over the duct and are not fastened to the ducts. Gaskets are positioned between the upstanding flange portions of the connectors and the upstanding flange portions of the ducts. The flanged connectors are bolted to each other with the flanged edge portions of the ducts therebetween. This type of connector is known as the "Vent stone" flange. The Vent stone flange is usually used with ducts fabricated from expensive material such as stainless steel and the like. Conventional steel L-shaped flanges can be used without compromising the interior stainless steel integrity of the duct. The above described known connectors for oval ducts require relatively accurate dimensions of the oval duct sections and substantial amounts of gasket and mastic gasket material to minimize leakage at the connections.
Another problem present with oval ducts is the distortion of the duct due either to the weight of the duct or the distortion of the duct by the pressure of the gas within the ducts. In FIG. 7, the distortion by the weight of the ducts is illustrated and in FIG. 8, the distortion by gas pressure is illustrated. It is desirable to provide a rigid connector for the ducts to minimize the distortion of the duct as illustrated in FIGS. 7 and 8 from breaking the seal at the connectors so that leakage does not occur at those locations.
There is a need for a duct connector for oval ducts which provides an airtight seal for the end portions of the oval duct sections and compensates for the variations in the dimensions of the oval duct and also provides rigidity and support for the end portions of each section so that the sections of oval ducts connected by the oval duct connectors are provided with a rigid frame-like support to minimize the distortions as illustrated in FIGS. 7 and 8.